The present invention relates generally to gyro-stabilized apparatus of the type employed, for example, on moving vehicles for providing a stabilized mounting platform for antennas, guns, optical devices, and the like, and more particularly to a method and an apparatus for overcoming certain destabilizing torques that may be applied to the platform.
In the prior art, one or more gyroscopes may be employed to provide stabilization (more particularly, short-term stabilization) of a platform, for example, about one or more rotational axes, such as pitch and roll axes. Usually, gyroscopic stabilization is employed in conjunction with some form of long-term "centralizing means" that provides steady-state or average direction or reference orientation of the platform. This centralizing means may provide a local vertical or horizontal reference, and may employ, for example, pendulums, springs, springs and mechanical linkages, or electrical torquers referenced to an external sensor.
Prior art stabilized platforms (that term being used herein to connote any stabilized structure or device) having one or more gyroscopes for stabilization of the platform about one or more axes are subject to destabilizing torques under certain conditions. For example, a typical ship-board platform stabilized about pitch and roll axes by platform-supported gyros may become destabilized when one of the gyros has its spin axis in a non-vertical orientation and the platform experiences angular motion in yaw (i.e., a change in azimuth relative to the meridian).
A closed-loop servo mechanism for slaving the platform to the ship's gyrocompass can provide a high degree of stabilization relative to the meridian. However, two stabilization problems may exist which are not completely resolved by this technique: namely, (1) destabilization due to uncompensated yaw in rapid or severe yaw motion, and (2) destabilization due to a cable "upwrap" maneuver that must be performed from time-to-time. The latter problem stems from the use of electrical cables connected to an apparatus on the platform from external equipment. Such cables acquire a cumulative twist due to relative azimuth motion between the ship and the platform over long periods of time and must be untwisted in a cable "unwrap" maneuver that involves rotating the platform by 180.degree. or 360.degree. in azimuth about its normally vertical axis.